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Annual motion of the sun.

  1. Feb 13, 2010 #1
    Ok, so the sun appears to move westward on a daily basis. But eastward through the stars on a yearly basis. I am supposed to explain both the daily and yearly motion of the sun using a few paragraphs with definitions and diagrams.

    For the year I basically have to explain and draw the sun's eliptic through the zodiac.

    Using a diagram like this.


    My question is, what direction is the sun moving in this diagram? It appears to be moving westward but cant I tell by the RA that it is really moving east?

    What it is really doing is lagging behind the stars right? Which makes it seem to drift eastward through them. And this is caused by precession?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 13, 2010 #2

    D H

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    You are looking at the diagram wrong.

    Imagine that you are laying on the ground at night looking upwards at the stars, with your body aligned north-south. In particular, your head is pointing to the north while your feet are pointing to the south. East is off to your *left*, not right. If you draw a star chart based on how you see things, you will naturally get a diagram with north at the top of the chart, south at the bottom, east to the left, and west to the right. This is a mirror image of directions on a map, where east is to the right and west is to the left.

    Answering those questions at this stage of the discussion would be a violation of this site's rules. We are supposed to help you do your own homework rather than do your homework for you.

    I can give you a hint: From the perspective of the Sun, the Earth is orbiting about the Sun, as are all the planets. From the perspective of the Earth, what is the Sun's motion?
  4. Feb 13, 2010 #3
    Thank you. The direction had been confusing me. So east will always be on the left on that diagram?

    The sun's motion appears to be westward across the sky on a daily basis... The "lagging" behind the sun is because of the earth's orbit around the sun... We are losing a degree a day due to earth's rotation in orbit around the sun. The earth has to rotate a little more to keep track with the sun then it does to keep track with the stars. Is what I have just described the effects of precession?
    Last edited: Feb 13, 2010
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